U-Shaped Ureadicarboxylic Acid as a Versatile Folding Unit for

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U-Shaped Ureadicarboxylic Acid as a Versatile Folding Unit for Construction of Zigzag-type Architecture Shugo Hisamatsu,† Hyuma Masu,‡ Isao Azumaya,§ Masahiro Takahashi,† Keiki Kishikawa,† and Shigeo Kohmoto*,† †

Department of Applied Chemistry and Biotechnology, Graduate School of Engineering, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan ‡ Chemical Analysis Center, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan § Faculty of Pharmaceutical Sciences at Kagawa Campus, Tokushima Bunri University, 1314-1 Shido, Sanuki, Kagawa 769-2193, Japan

bS Supporting Information ABSTRACT: U-shaped N,N0 -dimethyl-N,N0 -diphenylureadicarboxylic acid was developed as a folding unit to fabricate an H-bonding aromatic zigzag array. Recrystallization of it with dipyridyl derivatives gave cocrystals. Zigzag-type strands were formed by pinching dipyridyl derivatives via H-bonding with two carboxy moieties. Two types of H-bonding networks, helix and zigzag, were obtained depending on the structure of dipyridyl derivatives to be included. The former afforded a triple helix and the latter gave a twisted zigzag tape with chirality.

F

olding structures are commonly observed in nature and numerous attempts have been made to mimic this structure artificially.1 A variety of artificial aromatic foldamers have been prepared. Among them, we are interested in a zigzag-type one. The molecules are folded in a zigzag way with twisting, which generates a zigzag array with helicity. Urea,2 guanidine,3 and imide4 functionalities are utilized as U-shaped linkers to connect multiple aromatic moieties in a zigzag fashion. Owing to the folded face-to-face geometries of πstacked aromatic moieties, molecular wire behaviors of them can be expected.5 There is a conformational trick to construct zigzag type aromatic foldamers. For example, arylureas have an interesting conformational feature. Depending on the substituents at the nitrogen atoms, they adopt two distinctive conformations, either a linear or a folding conformation. Simple alteration of the substituent at the nitrogen atom from a hydrogen atom to a methyl group causes a drastic change in the conformation of urea compounds from the linear to the folding one.2a Our idea is to utilize this U-shaped building block for crystal engineering in order to construct zigzag-type architectures. We employed N,N0 -dimethyl-N,N0 -diphenylureadicarboxylic acid (1) as a folding unit which possessed two carboxy moieties as H-bonding sites. By sequential pinching of aromatic guest molecules with this folding unit, zigzag type architectures can be prepared. This methodology can offer a novel way of construction of the columnar array of aromatic components. Herein, we report on our approach to fabricate H-bonding zigzag architectures, which results in the formation of two types of them, triple helices by inclusion of 4,40 -dipyridyl (2), 1,2-di(4-pyridyl)ethylene (3), and 2,6di(pyridin-4yl)anthracene (4) and a chiral zigzag architecture from N-(pyridin-4-yl)isonicotinamide (5), respectively. Pyridine derivatives are well-known to associate with carboxylic acids by H-bonding. Supramolecules thus created are utilized for r 2011 American Chemical Society

liquid crystals6 and crystal engineering purposes.7 In some cases, helical arrays are generated with dicarboxylic acids.8 Resorcinol is also known to pinch pyridine derivatives as a template for solid-state photodimerization.7b,9 Figure 1 depicts our strategy for zigzag assembling by inclusion of dipyridyl derivatives which can be pinched by two carboxy moieties via H-bonding. There are two types of pinching in our case. In the first type, guest molecules are sandwiched by two neighboring carboxys attached to the upper faces and by those attached to the bottom faces of 1 (Figure 1a). In the second type, guest molecules are sandwiched by those attached to the upper and the bottom faces of 1 (Figure 1b). The former affords a helical and the latter gives a zigzag H-bonding network. In order to understand the folding structure of 1,10a single crystal X-ray diffraction analysis of it was carried out. Figure 2ac shows its ORTEP diagram, packing diagram, and H-bonding networks, respectively. The compound 1 has a folding structure with a U-shape. The molecule is twisted with the torsion angle of 58° between the two phenyl groups (Figure 2a). Two facing molecules of 1 are H-bonded to each other with a catemeric type H-bonding to create a dimeric unit. The dimeric units are H-bonded linearly to afford a chain-like structure (Figure 2b). Figure 2c shows the H-bonding networks observed in 1. Because of the torsion of the molecule, no dimeric type H-bonding between two carboxy groups exists. The molecules are linked with two catemeric H-bonding networks which create a rodlike structure with almost no cavity inside. The OO atomic distances in the double catemer are 2.64 and 2.65 Å. Received: February 28, 2011 Revised: March 22, 2011 Published: March 22, 2011 1453

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Figure 1. Schematic representation of two types of assemblies derived from the U-shaped building block 1. (a) Helical and (b) zigzag architectures.

Figure 2. Single crystal X-ray structure of 1. (a) ORTEP diagram. (b) The packing diagram with space-filling model showing the chain of the H-bonding dimer of 1 viewed along the b-axis. (c) The double catemeric structure created by H-bonding networks in which H-bonds are indicated with blue lines.

Cocrystals were obtained by recrystallization of 1 with dipyridyl derivatives. Recrystallization of 1 with 2, 3 (from methanol/water), and 4 (from ethanol/chloroform/hexane) afforded cocrystals 1 3 2,10b 1 3 3,10c and 1 3 4,10d respectively, in a ratio of the acid and the dipyridyl derivatives 1:1. Single crystal X-ray diffraction analysis of these cocrystals have shown that the complexes have triple helix structures in which three supramolecularly formed helical strands are assembled (Figure 3). Since the pioneering work by Lehn,11 a considerable

number of metal complexes of triple-stranded helicates have been synthesized. However, the examples of triple helix without an assistance of metal coordination are very limited.12 Figure 3a depicts the steps of the formation of triple helix for 1 3 2. In the first step, the compound 2 is sandwiched by two molecules of 1 with H-bonding between the carboxy moiety and the nitrogen atom of the pyridyl moiety. The remaining carboxy moiety is H-bonded with another molecule of 2. This repeating H-bonding in the second step creates a helical structure. The atomic distances between the nitrogen atom and the oxygen atom of the N 3 3 3 HO type H-bonding are 2.65 and 2.67 Å. The CdO 3 3 3 H interaction is also observed with the COH angle of 119°. The torsion angle between the two phenyl groups in the triple helix 1 3 2 (43°) is smaller than that of 1. The folding unit can adjust the torsion angle to the suitable one to create the triple helix. In the third step, three strands are assembled to give the triple helix. Their pitch and the width are 20.0 and 26.5 Å, respectively. It is a bilayer-plate with infinite length. Figure 3b shows its packing pattern. Cocrystal 1 3 3 afforded also a triple helix of the same type as that of 1 3 2 (Figure 3c). In the case of 1 3 3, disorder of the included 3 was observed. Two positions of 3 were observed in the ratio of 54:46. In the triple helix, the included 3 of the upper and the bottom layers are partially overlapped. Since the positions of nitrogen atoms are nearly the same in two positional isomers, both isomers can be fitted to the same triply helical structure. No disorder was found in the folding unit 1. The pitch and the width of triple helix 1 3 3 are 19.7 and 28.8 Å, respectively. It is interesting that even an inclusion of the molecule of different lengths results in the formation of triple helix. Because of almost the same width of the included molecules but with a different length, the resulting triple helices should have almost 1454

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Figure 3. Single crystal X-ray structures of triple helices 1 3 2, 1 3 3, and 1 3 4 in a space-filling model. Strands are colored with three different colors to distinguish each strand. (a) Schematic representation of the formation of triple helix 1 3 2. (b) Packing diagram of 1 3 2. Triple helices (c) 1 3 3 and (d) 1 3 4. In the cases of triple helices 1 3 3 and 1 3 4, one of the positions (major conformers) of disordered bipyridinyl derivatives is presented.

Figure 4. Fluorescence spectra of 4 (a) in solution and (b) in the solid state, and (c) that of 1 3 4 in the crystalline state. The inset figure shows the offset overlapping of the anthracene moieties in 1 3 4.

Figure 5. Single crystal X-ray structure of 1 3 5 3 (H2O)2. (a) Packing structure in which zigzag strands are colored differently. (c) Schematic representation of a twisted zigzag tape with chirality.

the same pitch but with a different width. This was further confirmed by the inclusion of the longer dipyridyl derivative 4 which possesses an anthracene moiety. The pitch of triple helix 1 3 4 (19.8 Å) remains almost the same as those of 1 3 2 and 1 3 3. However, its width is fairly longer than those of 1 3 2 and 1 3 3 (Figure 3d). Similar to the case of 1 3 3, disorder of the included 4 was observed. In order to examine the effect of overlapping on the fluorescence of 4, fluorescence spectra of 4 in solution, in the

solid state, and in the crystalline state of the complex 1 3 4 were measured (Figure 4). It is clear that fluorescence corresponding to the monomer emission was observed in its solution (Figure 4a), while the broad emission corresponding to the excimer emission was detected in its solid state (Figure 4b). Excimer emission becomes even broader and shifted slightly in a longer wavelength region in 1 3 4 (Figure 4c). Two neighboring 1455

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’ REFERENCES

Figure 6. CD spectra of 1 3 5 3 (H2O)2 in the solid state recorded on the KBr pellets derived from two different single crystals.

anthracene moieties in 1 3 4 are partial eclipsed. The inset shows the offset overlapping of the anthracene moieties observed in its X-ray structure. Because of this offset overlapping, a slight shift is resulted in fluorescence of 1 3 4. The cocrystal 1 3 5(H2O)210e is obtained as a dihydrate by recrystallization from methanol/water as chiral crystals with the space group C2221. Figure 5a show its packing structure. Disorder of included 5 was observed in two locations with the ratio of 1:1. No disorder was observed for 1. The way of H-bonding is different from those of 1 3 2, 1 3 3, and 1 3 4. The sequential H-bonding is operated in the manner as shown in Figure 1b, which gives a zigzag tape. The included 5 has a twisted structure in a single direction and the folding unit 1 has the unidirectional torsion, which furnishes a chirally twisted zigzag tape as schematically represented in Figure 5b. In order to confirm the chiral induction, a circular dicroism (CD) spectrum of 1 3 5 3 (H2O)2 in the solid state was recorded on its KBr pellet. Figure 6 shows its induced CD spectra. The opposite sign of the Cotton effect was observed from the sample of a different single crystal, which indicated that spontaneous chiral induction occurred during recrystallization and furnished conglomerate. In summary, we have developed N,N0 -dimethyl-N,N0 -diphenylureacarboxylic acid as a folding unit to create zigzag architectures in crystal engineering. Incorporation of dipyridyl derivatives afforded either a triple helix or a chirally twisted zigzag tape depending on the guest molecules to be included. The present methodology can be applied to the ordered arrangement of functional aromatic compounds.

’ ASSOCIATED CONTENT

bS

Supporting Information. Preparation information and spectral data of 1, and crystallographic information files (CIF) of 1, 1 3 2, 1 3 3, 1 3 4, and 1 3 5 3 (H2O)2. This material is available free of charge via the Internet at http://pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected].

’ ACKNOWLEDGMENT This work was partly supported by a Grant-in-Aid for Scientific Research (C) (No. 22550118) from the Japan Society for the Promotion of Science.

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(9) (a) MacGillivray, L. R.; Reid, J. L.; Ripmeester, J. A. J. Am. Chem. Soc. 2000, 122, 7817–7818. (b) Gao, X.; Friscic, T.; MacGillivray, L. R. Angew. Chem., Int. Ed. 2004, 43, 232–236. (10) (a) Crystal data for 1: C17H16N2O5, M = 328.32, triclinic, space group P1, a = 7.068(5), b = 8.481(6), c = 14.320(10) Å, R = 84.287(9), β = 78.229(9), γ = 69.272(8)°, V = 785.5(10) Å3, Z = 2, Dcalcd = 1.388 Mgm3, T = 250 K, μ = 0.104 mm1, GOF on F2 = 1.041, R1 = 0.0626, wR2 = 0.1812 (I > 2σ(I)). (b) Crystal data for 1 3 2: C17H16N2O5 3 C10H8N2, M = 484.50, monoclinic, space group P21/c, a = 20.222(2), b = 6.6626(7), c = 18.9969(19) Å, β = 114.0950(10)°, V = 2336.4(4) Å3, Z = 4, Dcalcd = 1.377 Mgm3, T = 150 K, μ = 0.097 mm1, GOF on F2 = 1.011, R1 = 0.0399, wR2 = 0.0588 (I > 2σ(I)). (c) Crystal data for 1 3 3: C17H16N2O5 3 C12H10N2, M = 510.54, monoclinic, space group P21/c, a = 21.787(2), b = 6.5789(7), c = 19.458(2) Å, β = 115.1360(10)°, V = 2524.8(5) Å3, Z = 4, Dcalcd = 1.343 Mg m3, T = 200 K, μ = 0.094 mm1, GOF on F2 = 1.038, R1 = 0.0448, wR2 = 0.0759 (I > 2σ(I)). (d) Crystal data for 1 3 4: C17H16N2O5 3 C24H16N2, M = 660.71, monoclinic, space group P21/c, a = 26.1395(11), b = 6.5856(3), c = 19.0470(7) Å, β = 101.757(3)°, V = 3210.5(2) Å3, Z = 4, Dcalcd = 1.367 Mg m3, T = 173 K, μ = 0.091 mm1, GOF on F2 = 1.066, R1 = 0.0805, wR2 = 0.1688 (I > 2σ(I)). (e) Crystal data for 1 3 5 3 (H2O)2: C17H16N2O5 3 C11H9N3O 3 2H2O, M = 563.56, orthorhombic, space group C2221, a = 11.0981(3), b = 11.5988(3), c = 21.6744(6) Å, V = 2790.03(13) Å3, Z = 4, Dcalcd = 1.342 Mg m3, T = 173 K, μ = 0.100 mm1, GOF on F2 = 1.039, R1 = 0.0592, wR2 = 0.1703 (I > 2σ(I)). (11) Kramer, R.; Lehn, J.-M.; DeCian, A.; Fischer, J. Angew. Chem., Int. Ed. Engl. 1993, 32, 703–706. (12) (a) Gulik-Krzywicki, T.; Fouquey, C.; Lehn, J.-M. Proc. Natl. Acad. Sci. U.S.A. 1993, 90, 163–176. (b) Lavender, E. S.; Ferguson, G.; Glidewell, C. Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 1999, 55, 430–432. (c) Dapporto, P.; Paoli, P.; Roelens, S. J. Org. Chem. 2001, 66, 4930–4933.

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